The present invention relates to a method for fabricating a semiconductor device, and more specifically to a method for fabricating a capacitor having a capacitor dielectric film formed of Ta2O5 (tantalum oxide) in a semiconductor device.
For microminiaturization of a semiconductor memory, it has become difficult to ensure a necessary capacitance only by increasing a surface area of a storage capacitor. Therefore, a method has been proposed which fabricates a semiconductor device having a capacitor having a capacitor dielectric film formed of Ta2O5 (tantalum oxide) which has a relative dielectric constant remarkably larger than that of SiN (silicon nitride) being used in the prior art. However, the Ta2O5 film has a problem that the Ta2O5 film is inferior to the SiN film in heat resistant property and a leak current is large.
In order to overcome this problem, IEEE Electron Device Letter, P514, 1989 proposes a semiconductor device fabricating method in which a Ta2O5 film is annealed in the presence of ultraviolet radiation and ozone (O3). Furthermore, Journal of Electrochemical Society, P1246, 1994 proposes a semiconductor device fabricating method in which a Ta2O5 film is treated with an oxygen plasma.
However, these proposals have another problem as follows: In the semiconductor device fabricating method proposed by IEEE Electron Device Letter, P514, 1989, since ultraviolet is irradiated to the whole of the device, reliability of transistors is deteriorated. In the semiconductor device fabricating method proposed by Journal of Electrochemical Society, P1246, 1994, the Ta2O5 film is damaged by the ion irradiation, and since the film quality cannot be improved over the whole surface of the capacitor dielectric film since ions and radials are not sufficiently uniformly irradiated in a coarse surface electrode structure.
Accordingly, it is an object of the present invention to provide a semiconductor device fabricating method which has overcome the above mentioned problems of the prior art.
Another object of the present invention is to provide a method for fabricating a capacitor having a capacitor dielectric film formed of Ta2O5 (tantalum oxide) in a semiconductor device, the method being capable of improving the film quality over the whole surface of the capacitor dielectric film to realize a capacitor having an excellent heat resistance property and a good leak current characteristics and at the same time capable of maintaining a good reliability of a transistor.
The above and other objects of the present invention are achieved in accordance with the present invention by a method for fabricating a capacitor having a capacitor dielectric film formed of Ta2O5 in a semiconductor device, the method comprising the step of:
forming a capacitor lower electrode on an insulating film formed on a semiconductor substrate;
forming a Ta2O5 film on the capacitor lower electrode;
immersing the semiconductor substrate into a H2O2 containing solution;
heat-treating the semiconductor substrate; and
forming a capacitor upper electrode on the Ta2O5 film.
In the above mentioned capacitor fabricating method in accordance with the present invention, the oxygen vacancy density in the Ta2O5 film is decreased by treating the Ta2O5 film with the H2O2 containing solution, with the result that the leak current of the capacitor having the capacitor dielectric film formed of Ta2O5 is reduced.
Furthermore, the film quality of the Ta2O5 film is improved by heat-treating the Ta2O5 film, with the result that the leak current of the capacitor having the capacitor dielectric film formed of Ta2O5 is reduced.
On the other hand, no ultraviolet radiation is carried out in the process for fabricating the capacitor and hence the semiconductor device having the capacitor. Therefore, it is possible to maintain a good reliability of the transistor, because the reliability of the transistor is in no way deteriorated by the ultraviolet radiation.
Since both the treatment with the H2O2 containing solution and the heat treatment are an isotropic reaction, the Ta2O5 film can be uniformly improved over the whole surface of the Ta2O5 film even in a coarse surface electrode structure.
In one embodiment of the capacitor fabricating method in accordance with the present invention, the heat-treatment is conducted at a temperature not less than 700xc2x0 C. Since crystallization of Ta2O5 occurs at the temperature not less than 700xc2x0 C., the film quality of the Ta2O5 film is greatly improved. Accordingly, the effect of reducing the leak current of the capacitor can further be enhanced.
In a preferred embodiment of the capacitor fabricating method in accordance with the present invention, the heat-treatment is conducted in an oxidizing atmosphere. When the heat-treatment is conducted in the oxidizing atmosphere, oxygen is effectively absorbed in the Ta2O5 film. Accordingly, the effect of reducing the leak current of the capacitor can further be enhanced.
In a specific embodiment of the capacitor fabricating method in accordance with the present invention, the heat-treatment is conducted in an oxygen containing atmosphere. Since the heat-treatment was conducted in the oxygen containing atmosphere, oxygen is effectively absorbed in the Ta2O5 film. Accordingly, the effect of reducing the leak current of the capacitor can further be enhanced.
In a preferred embodiment of the capacitor fabricating method in accordance with the present invention, the H2O2 containing solution has the H2O2 concentration not less than 5%. If the H2O2 concentration of the H2O2 containing solution is not less than 5%, reactivity for compensating the oxygen vacancy in the Ta2O5 film is intensified. Accordingly, the effect of reducing the leak current of the capacitor can further be enhanced.
In a more preferable embodiment of the capacitor fabricating method in accordance with the present invention, the temperature of the H2O2 containing solution is no less than 60xc2x0 C. If the temperature of the H2O2 containing solution is no less than 60xc2x0 C., reactivity for compensating the oxygen vacancy in the Ta2O5 film is intensified. Accordingly, the effect of reducing the leak current of the capacitor can further be enhanced.
In addition, the time of immersing the semiconductor substrate into the H2O2 containing solution is preferred to be not shorter than one minute, although the required immersing time depends upon the temperature of the H2O2 containing solution and the H2O2 concentration of the H2O2 containing solution.
The above and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings.